OsmoBTS Abis Protocol Specification

DRAFT

OsmoBTS Abis Protocol Specification i

sysmocom - s.f.m.c. GmbH

OsmoBTS Abis Protocol Specification

by Neels Hofmeyr and Harald Welte

Copyright © 2015-2016 sysmocom - s.f.m.c. GmbH

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License,Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts,and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".

The Asciidoc source code of this manual can be found at http://git.osmocom.org/osmo-gsm-manuals/

DRAFT v1-269-g908b, 2018-Jan-26

http://git.osmocom.org/osmo-gsm-manuals/

OsmoBTS Abis Protocol Specification ii

HISTORY

NUMBER DATE DESCRIPTION NAME

1 December 2015 Initial version, reflecting Os-moBTS master branch as on 2015-Dec-7 (commite28a20a2d9d049cd6312e218a7646593bbc43431).

NJH, HW

2 February 2016 Updated version with Message Sequence Chartof OML and RSL bring-up.

HW

2.1 February 2016 Fix A-bis OML/RSL port number swap inmessage seqeuence charts.

HW

2.2 July 2016 Add description on Dynamic ChannelConfiguration in OML and activation in RSL.

NJH, HW

Copyright © 2015-2016 sysmocom - s.f.m.c. GmbH DRAFT v1-269-g908b, 2018-Jan-26

OsmoBTS Abis Protocol Specification iii

Contents

1 Introduction 1

2 Overview 1

2.1 Identities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

3 IPA Multiplex 2

3.1 IPA Header . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3.2 IPA Stream Identifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3.3 IPA Connection Management (CCM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3.3.1 Identity Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3.3.2 IPA CCM Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

4 Organization & Maintenance Link (OML) 4

4.1 List of Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

4.1.1 Messages Compliant With TS 12.21 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

4.1.2 Messages Specific to OsmoBTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4.1.3 Messages Not Implemented by OsmoBTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4.2 Details on Compliant OML Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4.2.1 SW Activated Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4.2.2 Set BTS Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4.2.3 Set Radio Carrier Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

4.2.4 Set Channel Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

4.2.5 State Changed Event Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

4.2.6 Change Administrative State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

4.2.7 Opstart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4.3 Details on OsmoBTS Specific Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4.3.1 Set Attribute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4.4 Additional Object Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4.4.1 GPRS-NSE Managed Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4.4.2 GPRS Cell Managed Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4.4.3 GPRS NS-VC Managed Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4.5 Information Elements Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4.5.1 IEs Conforming to TS 12.21 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4.5.2 IEs Not Conforming to TS 12.21 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4.5.3 Additional Attributes and Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4.6 Details on IEs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4.6.1 HW Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4.6.2 ARFCN List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13


OsmoBTS Abis Protocol Specification iv

4.6.3 Additional Channel Combinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.6.4 Connection Failure Criterion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.6.5 TSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.6.6 RSL Destination IP Address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.6.7 RSL Destination TCP Port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.6.8 RSL IPA Stream ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.6.9 GPRS Routing Area Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.6.10 GPRS Paging Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.6.11 GPRS NSEI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.6.12 GPRS BVCI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.6.13 GPRS NSVCI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.6.14 GPRS NS Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.6.15 GPRS BSSGP Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.6.16 GPRS NS Link Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

4.6.17 GPRS RLC Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

4.6.18 GPRS Coding Schemes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

4.6.19 GPRS RLC Configuration 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4.6.20 GPRS RLC Configuration 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4.7 A-bis OML Initialization / BTS bring-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4.7.1 Site Manager MO Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

4.7.2 BTS MO Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

4.7.3 Baseband Transceiver MO Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

4.7.4 Radio Carrier MO Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

4.7.5 Channel MO Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4.7.6 Complete BTS Initialization Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

5 Radio Signalling Link (RSL) 25

5.1 List of Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

5.1.1 Messages Compliant With TS 08.58 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

5.1.2 Messages Specific to OsmoBTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

5.1.3 Messages Not Implemented by OsmoBTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

5.2 Message Limitation Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

5.2.1 Channel Activation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

5.2.2 Measurement Result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

5.2.3 Mode Modify . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

5.2.4 MS Power Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

5.2.5 SACCH Info Modify . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

5.2.6 BCCH Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

5.2.7 Channel Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29


OsmoBTS Abis Protocol Specification v

5.2.8 Paging Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

5.3 SMS Broadcast Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

5.3.1 RF Resource Indication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

5.3.2 SACCH Filling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

5.4 User Plane Transport Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

5.4.1 RSL Create Connection (CRCX) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

5.4.2 RSL Modify Connection (MDCX) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

5.4.3 RSL Delete Connection (DLCX) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

5.4.4 RSL Delete Connection (DLCX) Indication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

5.5 Dynamic Channel Combinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

5.5.1 IPA Style Dynamic Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

5.5.1.1 PDCH Activate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

5.5.1.2 PDCH Deactivate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

5.5.1.3 IPA Style Dynamic Switchover Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

5.5.2 Osmocom Style Dynamic Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

5.5.2.1 Osmocom Style Dynamic Switchover Example . . . . . . . . . . . . . . . . . . . . . . . . . 35

5.6 Message Formats and Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

5.6.1 Create Connection (CRCX) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

5.6.2 Create Connection (CRCX) ACK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

5.6.3 Create Connection (CRCX) NACK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

5.6.4 Modify Connection (MDCX) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

5.6.5 Modify Connection (MDCX) ACK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

5.6.6 Modify Connection (MDCX) NACK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

5.6.7 Delete Connection (DLCX) Indication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

5.6.8 Delete Connection (DLCX) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

5.6.9 Delete Connection (DLCX) ACK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

5.6.10 Delete Connection (DLCX) NACK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

5.6.11 PDCH Activate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

5.6.12 PDCH Activate ACK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

5.6.13 PDCH Activate NACK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

5.6.14 PDCH Deactivate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

5.6.15 PDCH Deactivate ACK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

5.6.16 PDCH Deactivate NACK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

5.7 Information Element Codings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

5.7.1 A-bis/IP specific RSL Message discriminators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

5.7.2 A-bis/IP specific RSL IEIs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

5.7.3 RSL_IE_CHAN_NR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

5.7.4 RSL_IE_IPAC_REMOTE_IP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

5.7.5 RSL_IE_IPAC_REMOTE_PORT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42


OsmoBTS Abis Protocol Specification vi

5.7.6 RSL_IE_IPAC_LOCAL_PORT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

5.7.7 RSL_IE_IPAC_SPEECH_MODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

5.7.8 RSL_IE_IPAC_LOCAL_IP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

5.7.9 RSL_IE_IPAC_CONN_STAT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

5.7.10 RSL_IE_IPAC_CONN_ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

5.7.11 RSL_IE_IPAC_RTP_PAYLOAD2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

5.8 A-bis RSL Initialization / BTS bring-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

6 User-Plane Traffic via RTP 44

6.1 RTP Payload Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

7 Glossary 45

A Osmocom TCP/UDP Port Numbers 51

B GNU Free Documentation License 52

B.1 PREAMBLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

B.2 APPLICABILITY AND DEFINITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

B.3 VERBATIM COPYING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

B.4 COPYING IN QUANTITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

B.5 MODIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

B.6 COMBINING DOCUMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

B.7 COLLECTIONS OF DOCUMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

B.8 AGGREGATION WITH INDEPENDENT WORKS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

B.9 TRANSLATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

B.10 TERMINATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

B.11 FUTURE REVISIONS OF THIS LICENSE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

B.12 RELICENSING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

B.13 ADDENDUM: How to use this License for your documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57


OsmoBTS Abis Protocol Specification 1 / 57

1 Introduction

This document describes the A-bis interface of OsmoBTS. Based on 3GPP TS 12.21 and 08.58, this document indicates whichof the 3GPP specified A-bis messages and IEs are implemented according to 3GPP specifications, which of these are not or notfully implemented, as well as OsmoBTS-specific extensions to the A-bis interface not specified by 3GPP.

Extensions to the A-bis interface specific to OsmoBTS are detailed in this document. For details on the messages and IEs thatcomply with above mentioned 3GPP specifications, please refer to those documents.

Table 1: 3GPP document versions referred to by this document

3GPP TS 08.56 version 8.0.1 Release 19993GPP TS 08.58 version 8.6.0 Release 19993GPP TS 08.60 version 8.2.1 Release 19993GPP TS 12.21 version 8.0.0 Release 1999

Table 2: IETF documents referred to by his document

IETF RFC 768 User Datagram ProtocolIETF RFC 791 Internet ProtocolIETF RFC 793 Transmission Control ProtocolIETF RFC 1889 RTP: A Transport Protocol for Real-Time ApplicationsIETF RFC 3551 RTP Profle for Audio and Video Conferences with Minimal ControlIETF RFC 4867 RTP Payload Format and Files Storage Format for the Adaptive Multi-Rate (AMR) and

Adaptive Multi-Rate Wideband (AMR-WB) Audio CodecsIETF RFC 5993 RTP Payload Format for Global Systems for Mobile Communications Half Rate (GSM-HR)

2 Overview

The OsmoBTS A-bis interface consists of traffic management messages (RSL, Radio Signalling Link) and network managementmessages (OML, Operation & Maintenance Link), encapsulated in an IPA multiplex.

OML and RSL each use a separate TCP connection.

Table 3: TCP port numbers used by OsmoBTS Abis/IP

TCP PortNumber

Usage

3002 A-bis OML (inside IPA multiplex)3003 A-bis RSL (inside IPA multiplex)

Both TCP connections for OML and RSL are established in the BTS→ BSC direction, i.e. the BTS is running as a TCP client,while the BSC is running as a TCP server.

The BTS first establishes the TCP connection for OML. Via OML, the BSC instructs the BTS to which IP address the RSLconnection shall be established.



Figure 1: Overview of A-bis connection establishment

2.1 Identities

The BTS is locally configured (via administrative means, out of band of this specification) to have a Unit ID. The Unit ID consistsof three parts:

• The Site Number

• The BTS number at the site

• The TRX number within the BTS

3 IPA Multiplex

The ETSI/3GPP specifications for A-bis transport (ETSI/3GPP TS 08.56) specify the transmission of RSL and OML messagesover a LAPD based framing on top of 64kBit/s signalling times slots (B-channels) on E1 lines.



OsmoBTS does not implement this LAPD based transport, but instead implements A-bis over IP in a flavor first observed byip.access nanoBTS products. The OsmoBTS implementation is a clean-room re-implementation based on the observation anddissection of protocol traces.

LAPD as used in E1 signalling channels provides in-order transmission and reliable delivery. This is why TCP was chosen asLayer 4 transport protocol on top of IP. TCP however, is a stream based transport protocol, which doesn’t preserve the boundariesof messages.

To work around this shortcoming, an additional framing layer called the IPA multiplex was introduced between TCP and theRSL and OML messages.

Table 4: Protocol Stacking

RSL + OML (this document)IPA (this document)TCP (IETF RFC 793)IP (IETF RFC 791)Ethernet (IEEE 802.3)

3.1 IPA Header

Each higher-layer PDU is encapsulated by a three-byte IPA header with the following structure:

Table 5: IPA Header Structure

Offset(Octets)

Length Name Description

0 2 Length Length of the variable-length payload section in network byte order(excluding the length of the IPA Header)

2 1 Stream Identifier Identifies the stream of the payload3 Variable Payload higher-layer PDU (i.e. RSL or OML message)

3.2 IPA Stream Identifiers

The IPA Stream Identifier serves to differentiate different streams within the multiplex. In the context of A-bis, it can be seen asanalogous to the LAPD TEI on classic A-bis over E1.

The following IPA stream identifiers are being used in A-bis/IP:

Table 6: IPA Stream Identifiers

Value (Hex) Name Description0x00 RSL A-bis RSL according to this document, TRX 00x01 RSL A-bis RSL according to this document, TRX 10x0n RSL A-bis RSL according to this document, TRX n0xfe CCM IPA Connection Management0xff OML A-bis OML according to this document



3.3 IPA Connection Management (CCM)

The IPA Connection Management is a sub-layer underneath the IPA multiplex which is used to manage the connection itself. Itsupports functions like Identity Management and Keep-Alive.

3.3.1 Identity Management

When a BTS connects to the BSC, the BSC must identify the connected BTS somehow. In ETSI/3GPP A-bis, the E1 multiplex +signalling timeslot number is used for this. In IP, there is no similar usable identity. Hence, the Unit ID is used for this purpose.

Table 7: Procedure for IPA peer identification is as follows

Direction OperationBTS→ BSC BTS connects the TCP connection to be used with IPABTS← BSC BSC requests BTS identity with ID_GETBTS→ BSC BTS responds BTS Unit ID with ID_RESPBTS← BSC BSC responds with ID_ACK, if the Unit ID is known to the BSC

Following the above peer identification procedure, transfer of higher-level messages such as OML or RSL commences.

3.3.2 IPA CCM Messages

IPA CCM supports the following messages

Table 8: IPA CCM Messages

Value Name Purpose0x00 PING Request a PONG from the peer0x01 PONG Response to a PING0x04 ID_GET Request Identity from peer0x05 ID_RESP Response to ID_GET0x06 ID_ACK Identity Acknowledged

4 Organization & Maintenance Link (OML)

4.1 List of Messages

The following tables list the OML messages used by OsmoBTS, grouped by their level of compliance with 3GPP TS 12.21.

4.1.1 Messages Compliant With TS 12.21

Specific limitations apply, see the linked sections.



Table 9: Messages compliant with TS 12.21

TS 12.21§

type code(hex)

This document § Message ←/→ Received/Sent byOsmoBTS

SW Download Management Messages:8.3.7 0x10 Section 4.2.1 SW Activated Report → SentAir Interface Management Messages:8.6.1 0x41 Section 4.2.2 Set BTS Attributes ← Received

0x42 Set BTS Attributes Ack → Sent0x43 Set BTS Attributes Nack → Sent

8.6.2 0x44 Section 4.2.3 Set Radio Carrier Attributes ← Received0x45 Set Radio Carrier Attributes Ack → Sent0x46 Set Radio Carrier Attributes Nack → Sent

8.6.3 0x47 Section 4.2.4 Set Channel Attributes ← Received0x48 Set Channel Attributes Ack → Sent0x49 Set Channel Attributes Nack → Sent

State Management and Event Report Messages:8.8.1 0x61 Section 4.2.5 State Changed Event Report → Sent8.8.5 0x69 Section 4.2.6 Change Administrative State ← Received

0x6A Change Administrative State Ack → Sent0x6B Change Administrative State Nack → Sent

Equipment Management Messages:8.9.2 0x74 Section 4.2.7 Opstart ← Received

0x75 Opstart Ack → Sent0x76 Opstart Nack → Sent

4.1.2 Messages Specific to OsmoBTS

Table 10: Messages specific to OsmoBTS, not found in 3GPP TS 12.21


Section 4.3.1 Set Attribute ← Received

4.1.3 Messages Not Implemented by OsmoBTS

Table 11: 3GPP TS 12.21 messages not implemented by OsmoBTS

TS 12.21 § type code(hex)

Message

SW Download Management Messages:8.3.1 0x01 Load Data Initiate

0x02 Load Data Initiate Ack0x03 Load Data Initiate Nack

8.3.2 0x04 Load Data Segment0x05 Load Data Segment Ack

8.3.3 0x06 Load Data Abort8.3.4 0x07 Load Data End

0x08 Load Data End Ack



Table 11: (continued)


Message

0x09 Load Data End Nack8.3.5 0x0A SW Activate Request

0x0B SW Activate Request Ack0x0C SW Activate Request Nack

8.3.6 0x0D Activate SW0x0E Activate SW Ack0x0F Activate SW Nack

A-bis Interface Management Messages:8.4.1 0x21 Establish TEI

0x22 Establish TEI Ack0x23 Establish TEI Nack

8.4.2 0x24 Connect Terrestrial Signalling0x25 Connect Terrestrial Signalling Ack0x26 Connect Terrestrial Signalling Nack

8.4.3 0x27 Disconnect Terrestrial Signalling0x28 Disconnect Terrestrial Signalling Ack0x29 Disconnect Terrestrial Signalling Nack

8.4.4 0x2A Connect Terrestrial Traffic0x2B Connect Terrestrial Traffic Ack0x2C Connect Terrestrial Traffic Nack

8.4.5 0x2D Disconnect Terrestrial Traffic0x2E Disconnect Terrestrial Traffic Ack0x2F Disconnect Terrestrial Traffic Nack

Transmission Management Messages:8.5.1 0x31 Connect Multi-Drop Link

0x32 Connect Multi-Drop Link Ack0x33 Connect Multi-Drop Link Nack

8.5.2 0x34 Disconnect Multi-Drop Link0x35 Disconnect Multi-Drop Link Ack0x36 Disconnect Multi-Drop Link Nack

Test Management Messages:8.7.1 0x51 Perform Test

0x52 Perform Test Ack0x53 Perform Test Nack

8.7.2 0x54 Test Report0x55 Send Test Report0x56 Send Test Report Ack

8.7.3 0x57 Send Test Report Nack8.7.4 0x58 Stop Test

0x59 Stop Test Ack0x5A Stop Test Nack

State Management and Event Report Messages:8.8.2 0x62 Failure Event Report8.8.3 0x63 Stop Sending Event Reports

0x64 Stop Sending Event Reports Ack0x65 Stop Sending Event Reports Nack

8.8.4 0x66 Restart Sending Event Reports0x67 Restart Sending Event Reports Ack0x68 Restart Sending Event Reports Nack

8.8.6 0x6C Change Administrative State Request0x6D Change Administrative State Request Ack0x6E Change Administrative State Request Nack

8.8.7 0x93 Report Outstanding Alarms





Message

0x94 Report Outstanding Alarms Ack0x95 Report Outstanding Alarms Nack

Equipment Management Messages:8.9.1 0x71 Changeover

0x72 Changeover Ack0x73 Changeover Nack

8.9.3 0x87 Reinitialize0x88 Reinitialize Ack0x89 Reinitialize Nack

8.9.4 0x77 Set Site Outputs0x78 Set Site Outputs Ack0x79 Set Site Outputs Nack

8.9.5 0x90 Change HW Configuration0x91 Change HW Configuration Ack0x92 Change HW Configuration Nack

Measurement Management Messages:8.10.1 0x8A Measurement Result Request8.10.2 0x8B Measurement Result Response8.10.3 0x8C Stop Measurement8.10.4 0x8D Start MeasurementOther Messages:8.11.1 0x81 Get Attributes8.11.3 0x82 Get Attribute(s) Response8.11.1 0x83 Get Attributes Nack8.11.2 0x84 Set Alarm Threshold

0x85 Set Alarm Threshold Ack0x86 Set Alarm Threshold Nack

4.2 Details on Compliant OML Messages

4.2.1 SW Activated Report

OsmoBTS will send an SW Activated Report when RF has been activated successfully. The message is compliant with 3GPP TS12.21 § 8.3.7.

Upon RF activation, two SW Activated Report messages will be sent, for the Object Classes

• Radio Carrier (0x02)

• Baseband Transceiver (0x04)

4.2.2 Set BTS Attributes

OsmoBTS will receive a Set BTS Attributes message and reply with a corresponding ACK message on success. IE handling isfully compliant to TS 12.21, except that a change of BCCH ARFCN or BSIC while in operation is not supported, and hence theStarting Time IE is rejected.



Table 12: Set BTS Attributes IEs not handled by OsmoBTS

TS 12.21 § IE Name Handling9.4.52 Starting Time not supported (provokes NACK cause 0x10)

4.2.3 Set Radio Carrier Attributes

This message conforms to 3GPP TS 12.21, with the following limitation, as frequency hopping is not supported by OsmoBTS:

Table 13: Set Radio Carrier Attributes IE limitations

TS 12.21 § IE Name Handling9.4.5 ARFCN List ignored

4.2.4 Set Channel Attributes

This message conforms to 3GPP TS 12.21, with the following limitation: the following 3GPP TS 12.21 IEs provoke a NACKresponse when sent to OsmoBTS, as frequency hopping is not supported:

Table 14: Set Channel Attributes IE limitations

TS 12.21 § IE Name Handling9.4.21 HSN not supported (provokes NACK cause 0x10)9.4.27 MAIO not supported (provokes NACK cause 0x10)9.4.52 Starting Time not supported (provokes NACK cause 0x10)

4.2.5 State Changed Event Report

This message is compliant with 3GPP TS 12.21. Exactly these IEs are sent by OsmoBTS:

INFORMATION ELEMENT REFERENCE PRESENCE FORMAT LENGTHMessage Type (0xf5) 3GPP TS 12.21 9.1 M V 1Object Class 3GPP TS 12.21 9.2 M V 1Object Instance 3GPP TS 12.21 9.3 M V 3Operational State 3GPP TS 12.21 9.4.38 O TV 2Availability Status 3GPP TS 12.21 9.4.7 O TL16V (with

length of 1)3

4.2.6 Change Administrative State

This message is compliant with 3GPP TS 12.21 § 8.8.5. It applies to all of the Object Classes defined in 3GPP TS 12.21 § 9.2 aswell as Section 4.4.



4.2.7 Opstart

This message is compliant with 3GPP TS 12.21 § 8.9.2. It applies to all of the Object Classes defined in 3GPP TS 12.21 § 9.2 aswell as Section 4.4.

4.3 Details on OsmoBTS Specific Messages

4.3.1 Set Attribute

The message type is 0xf5. This message is sent to OsmoBTS to set attributes on instances of managed objects of the non-standardadditional Object Classes (see Section 4.4).

The message specifics depend on the Object Class and are detailed in Section 4.4.

INFORMATION ELEMENT REFERENCE PRESENCE FORMAT LENGTHMessage Type (0xf5) 3GPP TS 12.21 9.1 M V 1Object Class 3GPP TS 12.21 9.2 M V 1Object Instance 3GPP TS 12.21 9.3 M V 3Object Class specific IEs follow, see Section 4.4. . .

4.4 Additional Object Classes

In addition to 3GPP TS 12.21 Chapter 9.2, the following managed objects are supported:

Table 15: Additional Managed Object Classes

Value Name Description0xf0 GPRS NSE GPRS-NS Entity0xf1 GPRS CELL GPRS Cell Entity0xf2 GPRS NSVC GPRS NS Virtual Circuit

4.4.1 GPRS-NSE Managed Object

There is one NS Entity per BTS. It supports the Set Attribute message with the following Information Elements:

INFORMATION ELEMENT REFERENCE PRESENCE FORMAT LENGTHMessage Type 3GPP TS 12.21 9.1 M V 1Object Class 3GPP TS 12.21 9.2 M V 1Object Instance 3GPP TS 12.21 9.3 M V 3GPRS NSEI Section 4.6.11 O TL16V >= 5GPRS NS Configuration Section 4.6.16 O TL16V >= 10GPRS BSSGP Configuration Section 4.6.15 O TL16V >= 14

4.4.2 GPRS Cell Managed Object

There is one GPRS Cell entity per BTS. It supports the Set Attribute message with the following Information Elements:

INFORMATION ELEMENT REFERENCE PRESENCE FORMAT LENGTHMessage Type 3GPP TS 12.21 9.1 M V 1Object Class 3GPP TS 12.21 9.2 M V 1



INFORMATION ELEMENT REFERENCE PRESENCE FORMAT LENGTHObject Instance 3GPP TS 12.21 9.3 M V 3GPRS Routing Area Code Section 4.6.9 O TL16V >= 4GPRS Paging Configuration Section 4.6.10 O TL16V >= 5GPRS RLC Configuration Section 4.6.17 O TL16V >= 12GPRS Coding Schemes Section 4.6.18 O TL16V >= 5GPRS RLC Configuration 2 Section 4.6.19 O TL16V >= 8GPRS RLC Configuration 3 Section 4.6.20 O TL16V >= 4

4.4.3 GPRS NS-VC Managed Object

There are two GPRS NS-VC instances per BTS. It supports the Set Attribute message with the following Information Elements:

INFORMATION ELEMENT REFERENCE PRESENCE FORMAT LENGTHMessage Type 3GPP TS 12.21 9.1 M V 1Object Class 3GPP TS 12.21 9.2 M V 1Object Instance 3GPP TS 12.21 9.3 M V 3GPRS NSVCI Section 4.6.13 O TL16V >= 5GPRS NS Link Configuration Section 4.6.16 O TL16V >= 11

4.5 Information Elements Overview

All of the IEs handled by OsmoBTS are listed below, with limitations and additions to TS 12.21 specified in more detail.

4.5.1 IEs Conforming to TS 12.21

The following Information Elements are accepted by OsmoBTS.

IEs marked ignored may be sent to OsmoBTS without causing error conditions. These IEs are skipped during message parsingand are never evaluated.

IEs marked ignored and additionally marked as being received by OsmoBTS (←) are in fact parsed and their values are storedby OsmoBTS, but these stored items are currently not used in the OsmoBTS code base.

Table 16: IEs conforming to TS 12.21

tag(hex)

TS 12.21§

IE name ←/→ Received/Sent by OsmoBTS

0x00 9.4.1 Abis Channel ignored0x01 9.4.2 Additional Info ignored0x02 9.4.3 Additional Text ignored0x03 9.4.4 Administrative State ←

→Received & Sent

0x04 9.4.5 ARFCN List ← Received, with exactly 1 ARFCN: seeSection 4.6.2; ignored by Set RadioAttribute message (Section 4.2.3)

0x05 9.4.6 Autonomously Report ignored0x06 9.4.7 Availability Status → Sent0x07 9.4.8 BCCH ARFCN ← Received0x08 9.4.9 BSIC ← Received0x09 9.4.10 BTS Air Timer ← Received0x0a 9.4.11 CCCH Load Indication Period ← Received0x0b 9.4.12 CCCH Load Threshold ← Received0x0c 9.4.13 Channel Combination ← Received, with additional channel

combinations: see Section 4.6.3




tag(hex)

TS 12.21§

IE name ←/→ Received/Sent by OsmoBTS

0x0d 9.4.14 Connection Failure Criterion ← Received, with limitations see Section 4.6.40x0e 9.4.15 Destination ignored0x0f 9.4.16 Event Type ignored0x11 9.4.17 File Data ignored0x12 9.4.18 File Id ignored0x13 9.4.19 File Version ignored0x14 9.4.20 GSM Time ignored0x16 9.4.22 HW Configuration ignored0x18 9.4.24 Intave Parameter ← ignored0x19 9.4.25 Interference level Boundaries ← ignored0x1a 9.4.26 List of Required Attributes ignored0x1c 9.4.28 Manufacturer Dependent State ignored0x1d 9.4.29 Manufacturer Dependent Thresholds ignored0x1e 9.4.30 Manufacturer Id ignored0x1f 9.4.31 Max Timing Advance ← Received0x20 9.4.34 Multi-drop BSC Link ignored0x21 9.4.35 Multi-drop next BTS Link ignored0x22 9.4.36 Nack Causes → Sent0x23 9.4.37 Ny1 ← Received0x24 9.4.38 Operational State → Sent0x25 9.4.39 Overload Period ← ignored0x26 9.4.40 Physical Config ignored0x27 9.4.41 Power Class ignored0x28 9.4.42 Power Output Thresholds ignored0x29 9.4.43 Probable Cause ignored0x2a 9.4.44 RACH Busy Threshold ← Received0x2b 9.4.45 RACH Load Averaging Slots ← ignored0x2c 9.4.46 Radio Sub Channel ignored0x2d 9.4.47 RF Max Power Reduction ← Received0x2e 9.4.48 Site Inputs ignored0x2f 9.4.49 Site Outputs ignored0x30 9.4.50 Source ignored0x31 9.4.51 Specific Problems ignored0x33 9.4.53 T200 ← ignored (1s on DCCH, 2s on ACCH)0x34 9.4.54 TEI ignored0x35 9.4.55 Test Duration ignored0x36 9.4.56 Test No ignored0x37 9.4.57 Test Report Info ignored0x38 9.4.58 VSWR Thresholds ignored0x39 9.4.59 Window Size ignored0x40 9.4.60 TSC ← Received, with limitations: see

Section 4.6.50x41 9.4.61 SW Configuration ignored0x43 9.4.63 Perceived Severity ignored0x44 9.4.64 Get Attribute Response Info ignored0x45 9.4.65 Outstanding Alarm Sequence ignored0x46 9.4.66 HW Conf Change Info ignored0x47 9.4.32 Measurement Result ignored



4.5.2 IEs Not Conforming to TS 12.21

Table 17: IEs not conforming to TS 12.21

tag(hex)

TS 12.21 § IE name Description

0x15 9.4.21 HSN presence causes NACK response0x17 9.4.23 HW Description ignored by OsmoBTS, but coding may differ, see

Section 4.6.10x1b 9.4.27 MAIO presence causes NACK response0x32 9.4.52 Starting Time presence causes NACK response0x42 9.4.62 SW Description not supported0x48 9.4.33 Measurement Type not supported

4.5.3 Additional Attributes and Parameters

The following Information Elements are defined in addition to those specified in 3GPP TS 12.21 Chapter 9.4.

All of these additional IEs are received by OsmoBTS.

These attributes are not used by OsmoBTS, but simply passed to OsmoPCU connected to the PCU socket.

Table 18: Additional IEs handled by OsmoBTS but not defined in TS12.21

tag(hex)

IE name Description

0x80 RSL Destination IP Address Section 4.6.60x81 RSL Destination TCP Port Section 4.6.70x85 RSL IPA Stream ID Section 4.6.80x9a GPRS Routing Area Code Section 4.6.90x9c GPRS Paging Configuration Section 4.6.100x9d GPRS NSEI Section 4.6.110x9e GPRS BVCI Section 4.6.120x9f GPRS NSVCI Section 4.6.130xa0 GPRS NS Configuration Section 4.6.140xa1 GPRS BSSGP Configuration Section 4.6.150xa2 GPRS NS Link Configuration Section 4.6.160xa3 GPRS RLC Configuration Section 4.6.170xa8 GPRS Coding Schemes Section 4.6.180xa9 GPRS RLC Configuration 2 Section 4.6.190xac GPRS RLC Configuration 3 Section 4.6.20

4.6 Details on IEs

4.6.1 HW Description

TS 12.21 suggests a series of 5 length-value pairs for the HW Description IE. Instead, OsmoBTS interprets it as a single TL16V.The value of this IE is ignored by OsmoBTS, yet the coding may affect message parsing.



Attribute Identifier (0x17) 1Length 2-3Ignored N

4.6.2 ARFCN List

Since OsmoBTS does not support frequency hopping, the ARFCN List must contain exactly one ARFCN.

4.6.3 Additional Channel Combinations

In addition to 3GPP TS 12.21 Chapter 9.4.13, the following channel combinations are supported:

Table 19: Additional Channel Combinations

Value Description0x0b Reserved for PBCCH + PCCCH + PDTCH/F + PACCH/F + PTCCH/F0x0c Reserved for PBCCH + PDTCH/F + PACCH/F + PTCCH/F0x0d PDTCH/F + PACCH/F + PTCCH/F0x80 ip.access style Dynamic TCH/F / PDCH0x81 Reserved for Dynamic TCH/F / TCH/H0x90 Osmocom style Dynamic TCH/F / TCH/H / PDCH

The Reserved combinations are not actually supported/implemented yet, but merely reserved for such functionality, if it iseventually implemented.

For more information on how the different dynamic channel combinations work, please see the Section 5.5.

4.6.4 Connection Failure Criterion

3GPP TS 12.21 Chapter 9.4.14 specifies two different options for the Connection Failure Criterion. OsmoBTS only implementsthe option coded as 0x01, i.e. based upon uplink SACCH error rate (RADIO_LINK_TIMEOUT).

4.6.5 TSC

Due to limitations in the currently supported PHY implementations, OsmoBTS supports only one global TSC for all channels onone TRX, rather than a separate TSC for each timeslot, as expected by 3GPP TS 12.21.

4.6.6 RSL Destination IP Address

The value part of this attribute has a length of 4 octets and is encoded as IPv4 address in network byte order.

Attribute Identifier (0x80) 1IPv4 Address (MSB first) 2-5

4.6.7 RSL Destination TCP Port

The value part of this attribute has a length of 2 octets and contains the TCP destination port for the RSL connection, encoded innetwork byte order.



Attribute Identifier (0x81) 1Port number (MSB first) 2-3

4.6.8 RSL IPA Stream ID

The value part of this attribute has a length of one octet and specifies the IPA stream ID to be used for the RSL connection of thisTRX.

Attribute Identifier (0x85) 1Stream ID 2

4.6.9 GPRS Routing Area Code

The value part of the GPRS Routing Area code consists of a single octet encoding the GPRS Routing Area Code.

This attribute is not used by OsmoBTS, but simply passed to OsmoPCU connected to the PCU socket.

4.6.10 GPRS Paging Configuration

The value part of this attribute consists of two octets encoded as follows:

Offset Description0 GPRS Paging repeat time in units of 50ms intervals1 GPRS Paging repeat count

4.6.11 GPRS NSEI

The value part of the GPRS NSEI is encoded as 16bit integer value in network byte order.


4.6.12 GPRS BVCI

The value part of this attribute consists of two octets encoding the BSSGP Virtual Circuit Identifier (BVCI) as unsigned 16 bitinteger in network byte order.

4.6.13 GPRS NSVCI

The value part of the GPRS NSVCI attribute is a 16bit unsigned integer in network byte order, encoding the GPRS NSVCI asspecified in 3GPP TS 08.16.


4.6.14 GPRS NS Configuration

The value part of the GPRS NS Configuration consists of an array of 7 octets, each describing one GPRS NS related timer:


4.6.15 GPRS BSSGP Configuration

The value part of the GPRS BSSGP configuration consists of an array of 11 octets, each describing one GPRS BSSGP relatedtimer:



Offset Description0 Blocking Timer (T1)1 Blocking Retries2 Unblocking Retries3 Reset Timer (T2)4 Reset Retries5 Suspend Timer (T3) in units of 100ms6 Suspend Retries7 Resume Timer (T4) in units of 100ms8 Resume Retries9 Capability Update Timer (T5)10 Capability Update Retries

The detailed description of the meaning of those timers is given in the GPRS BSSGP specification 3GPP TS 08.18.


4.6.16 GPRS NS Link Configuration

This attribute is 8 octets long and encoded as follows:

Offset Length Description0 2 GPRS-NS Remote UDP Port Number (SGSN side)2 4 GPRS-NS Remote IPv4 Address (SGSN side)6 2 GPRS-NS Local UDP Port Number (BTS side)

All values are encoded in network byte order.


4.6.17 GPRS RLC Configuration

The value part of the GPRS RLC Configuration consists of an array of 9 octets, each describing a RLC timer:

Offset Description Unit0 GPRS RLC Timer T3142 s1 GPRS RLC Timer T3169 s2 GPRS RLC Timer T3191 s3 GPRS RLC Timer T3193 10ms4 GPRS RLC Timer T3195 s5 GPRS RLC Timer T3101 s6 GPRS RLC Timer T3103 s7 GPRS RLC Timer T3105 s8 GPRS RLC CV Countdown -

The meaning of the RLC timers are specified in 3GPP TS 04.60.

The countdown value specifies the RLC CV value from which the countdown procedure is started.


4.6.18 GPRS Coding Schemes

The value part of the GPRS Coding Schemes consists of two octets encoding the available GPRS and EDGE coding schemes.



bit 7 6 5 4 3 2 1 0byte atoffset 0

MCS9 x x x CS4 CS3 CS2 CS1

byte atoffset 1

MCS8 MCS7 MCS6 MCS5 MCS4 MCS3 MCS2 MCS1


4.6.19 GPRS RLC Configuration 2

The value part of this attribute is 8 octets long and encoded as follows:

Offset Length Description Unit0 2 Downlink TBF Extension Timer 10ms2 2 Uplink TBF Extension Timer 10ms4 2 Initial GPRS Coding Scheme -

The Initial GPRS Coding Scheme is encoded as follows:

Value Description1 CS 12 CS 23 CS 34 CS 4


4.6.20 GPRS RLC Configuration 3

This attribute contains information about the initial MCS used for new EDGE TBFs.

It is encoded as follows:

Value Description1 MCS 12 MCS 23 MCS 34 MCS 45 MCS 56 MCS 67 MCS 78 MCS 89 MCS 9


4.7 A-bis OML Initialization / BTS bring-up

At the time an Abis/IP BTS connects to via OML to the BSC, it is initialized according to the procedures described in 3GPP TS12.21 as amended by this document.

Each Managed Object (MO) is separately initialized. The initialization sequence and parameters differ slightly depending on theMO involved.



Some parts of the sequences described below are optional, such as the Software activation. In the OsmoBTS case, the softwareis not modular and thus all MOs start with the software fully activated. In effect, no Software Activate Request is being sent bythe MO to the BSC, nor does the BSC need to initialize the Activate Software procedure.

Still, the full sequences are shown in order to explain the Abis/IP protocol.

Also, the initial state of the MOs at time of OML connection initialization is not always guaranteed to be Disabled/Notinstalled.Rather, the BSC implementation has to deal with the initial state as reported by the MOs at time of re-connection.

4.7.1 Site Manager MO Initialization

Figure 2: A-bis OML Initialization of Site Manager MO

The Site Manager MO does not depend on other MOs, nor does it have an Administrative state (Locked/Unlocked), thus itimmediately commences in the Enabled state.



4.7.2 BTS MO Initialization

Figure 3: A-bis OML Initialization of BTS MO

As shown in the BTS MO, its state is

• Availability state Dependency, meaning it depends on other MOs to be initialized before becoming enabled.

• Administrative state Locked, as the object is first waiting to receive attributes in the Locked state, before the Change Adminis-trative State (Unlocked) procedure is used to request transitioning into Unlocked state.



4.7.3 Baseband Transceiver MO Initialization

Figure 4: A-bis OML Initialization of Baseband Transceiver MO

There is one Baseband Transceiver MO per TRX in the BTS. For a multi-TRX BTS, the above procedure must be repeated foreach TRX.



4.7.4 Radio Carrier MO Initialization

Figure 5: A-bis OML Initialization of Radio Carrier MO

There is one Radio Carrier MO per TRX in the BTS. For a multi-TRX BTS, the above procedure must be repeated for each TRX.



4.7.5 Channel MO Initialization

Figure 6: A-bis OML Initialization of Radio Carrier MO

There are 8 timeslots in each TRX, and correspondingly 8 Channel MOs in every TRX. The above procedure must thus berepeated for each timeslot in each transceiver of the BTS.

4.7.6 Complete BTS Initialization Procedure

Some of below steps are optional, as is their detailed ordering. In practice, the procedures for different MOs may overlap. Themessage sequence charts in this document have been hand-crafted to avoid such overlap for the sake of clarity.



Figure 7: A-bis OML BTS bring-up (1/3)

As shown in Figure 7, after the OML TCP connection is established,

1. the identity is exchanged via IPA CCM,

2. the BTS sends an OML EVENT STATE CHANGED REPORT for every Managed Object, and

3. the BTS subsequently requests the activation of its Site Manager Object which the BSC performs by the Activate SWcommand.

4. After successful activation of the software in the Site Manager,

a. the state changes to Enabled, and an event report is generated accordingly, and

b. the BSC is notified about the SW activation in an associated report.

5. Finally, the BSC requests the start of the Site Manager

a. using the OPSTART command,

b. which is subsequently acknowledged by the Site Manager.







Figure 8 shows:

1. Software Activation and associated state transitions of the BTS MO;



2. Setting of the BTS Attributes followed by OPSTART;

3. Software Activation and associated state transitions of the Baseband Transceiver MO;

4. Software Activation and associated state transitions of the Radio Carrier MO;

5. Once the Baseband Transceiver MO has its software activated, the Channel MOs (one for each timeslot) indicate theirstate change as well as software activation.

Figure 9 shows:

1. The Radio Carrier MO Software Activation;

2. The Request to the Baseband Transceiver MO to establish the RSL signalling connection to the BSC;

3. Subsequent OPSTART and Change of Administrative State on the Baseband Transceiver MO;

4. The following procedure takes place for each of the Channel MOs:

a. Set the Channel Attributes (such as channel combination),

b. OPSTART,

c. change the Administrative State to Unlocked,

d. followed by a State Change Event Report with the new state.

5. After all Channel MOs are initialized, the Radio Carrier goes through a similar procedure:

a. Set attributes,

b. OPSTART,

c. change Administrative State to Unlocked,

d. followed by a State Change Event Report with the new State (Enabled/OK)

6. All Channel MOs now also report their state as Enabled/OK.

7. Finally, the BTS reports its state as Enabled/OK.

5 Radio Signalling Link (RSL)

5.1 List of Messages

The following tables list the RSL messages used by OsmoBTS A-bis/IP, grouped by their level of compliance with 3GPP TS08.58.

5.1.1 Messages Compliant With TS 08.58

Specific additions and limitations apply, see the linked sections.

Table 20: Messages compliant with TS 08.58

TS 08.58§


Radio link layer management messages8.3.1 - DATA REQUEST ← Received8.3.2 - DATA INDICATION → Sent8.3.3 - ERROR INDICATION → Sent8.3.4 - ESTABLISH REQUEST ← Received




TS 08.58§


8.3.5 - ESTABLISH CONFIRM → Sent8.3.6 - ESTABLISH INDICATION → Sent8.3.7 - RELEASE REQUEST ← Received8.3.8 - RELEASE CONFIRM → Sent8.3.9 - RELEASE INDICATION → Sent8.3.10 - UNIT DATA REQUEST ← Received8.3.11 - UNIT DATA INDICATION → SentDEDICATED CHANNEL MANAGEMENT MESSAGES8.4.1 Section 5.2.1 CHANNEL ACTIVATION ← Received8.4.2 Section 5.2.1 CHANNEL ACTIVATION ACKNOWLEDGE → Sent8.4.3 Section 5.2.1 CHANNEL ACTIVATION NEGATIVE

ACKNOWLEDGE→ Sent

8.4.4 - CONNECTION FAILURE INDICATION → Sent8.4.5 - DEACTIVATE SACCH ← Received8.4.6 - ENCRYPTION COMMAND ← Received8.4.7 - HANDOVER DETECTION → Sent8.4.8 Section 5.2.2 MEASUREMENT RESULT → Sent8.4.9 Section 5.2.3 MODE MODIFY ← Received8.4.10 - MODE MODIFY ACKNOWLEDGE → Sent8.4.11 - MODE MODIFY NEGATIVE

ACKNOWLEDGE→ Sent

8.4.14 - RF CHANNEL RELEASE ← Received8.4.15 Section 5.2.4 MS POWER CONTROL ← Received8.4.19 - RF CHANNEL RELEASE ACKNOWLEDGE → Sent8.4.20 Section 5.2.5 SACCH INFO MODIFY ← ReceivedCOMMON CHANNEL MANAGEMENT MESSAGES8.5.1 Section 5.2.6 BCCH INFORMATION ← Received8.5.2 - CCCH LOAD INDICATION → Sent8.5.3 Section 5.2.7 CHANNEL REQUIRED → Sent8.5.5 Section 5.2.8 PAGING COMMAND ← Received8.5.6 - IMMEDIATE ASSIGN COMMAND ← Received8.5.8 Section 5.3 SMS BROADCAST COMMAND ← ReceivedTRX MANAGEMENT MESSAGES8.6.1 Section 5.3.1 RF RESOURCE INDICATION → Sent8.6.2 Section 5.3.2 SACCH FILLING ← Received8.6.4 - ERROR REPORT → Sent

5.1.2 Messages Specific to OsmoBTS

Table 21: Messages specific to OsmoBTS, not found in 3GPP TS 08.58


User Plane Transport Management (Section 5.4)Section 5.4.1 Section 5.6.1 RSL Create Connection (CRCX) ← Received

Section 5.6.2 RSL Create Connection (CRCX) ACK → SentSection 5.6.3 RSL Create Connection (CRCX) NACK → Sent

Section 5.4.2 Section 5.6.4 RSL Modify Connection (MDCX) ← ReceivedSection 5.6.5 RSL Modify Connection (MDCX) ACK → Sent





Section 5.6.6 RSL Modify Connection (MDCX) NACK → SentSection 5.4.3 Section 5.6.8 RSL Delete Connection (DLCX) ← Received

Section 5.6.9 RSL Delete Connection (DLCX) ACK → SentSection 5.6.10 RSL Delete Connection (DLCX) NACK → Sent

Section 5.4.4 Section 5.6.7 RSL Delete Connection (DLCX) Indication → SentIPA style PDCH Management (Section 5.5.1)Section 5.5.1.1 Section 5.6.11 RSL PDCH Activation ← Received

Section 5.6.12 RSL PDCH Activation ACK → SentSection 5.6.13 RSL PDCH Activation NACK → Sent

Section 5.5.1.2 Section 5.6.14 RSL PDCH Deactivation ← ReceivedSection 5.6.15 RSL PDCH Deactivation ACK → SentSection 5.6.16 RSL PDCH Deactivation NACK → Sent

5.1.3 Messages Not Implemented by OsmoBTS

Table 22: 3GPP TS 08.58 messages not implemented by OsmoBTS

TS 08.58 § MessageDEDICATED CHANNEL MANAGEMENT MESSAGES8.4.12 PHYSICAL CONTEXT REQUEST8.4.13 PHYSICAL CONTEXT CONFIRM8.4.16 BS POWER CONTROL8.4.17 PREPROCESS CONFIGURE8.4.18 PREPROCESSED MEASUREMENT RESULT8.4.21 TALKER DETECTION8.4.22 LISTENER DETECTION8.4.23 REMOTE CODEC CONFIGURATION REPORT8.4.24 ROUND TRIP DELAY REPORT8.4.25 PRE-HANDOVER NOTIFICATION8.4.26 MULTIRATE CODEC MODIFICATION REQUEST8.4.27 MULTIRATE CODEC MODIFICATION ACKNOWLEDGE8.4.28 MULTIRATE CODEC MODIFICATION NEGATIVE ACKNOWLEDGE8.4.29 MULTIRATE CODEC MODIFICATION PERFORMED8.4.30 TFO REPORT8.4.31 TFO MODIFICATION REQUESTCOMMON CHANNEL MANAGEMENT MESSAGES8.5.4 DELETE INDICATION8.5.7 SMS BROADCAST REQUEST8.5.9 CBCH LOAD INDICATION8.5.10 NOTIFICATION COMMANDTRX MANAGEMENT MESSAGES8.6.3 OVERLOADLOCATION SERVICES MESSAGES8.7.1 LOCATION INFORMATION



5.2 Message Limitation Details

5.2.1 Channel Activation

When used on a timeslot using the non-standard channel combination NM_CHANC_OSMO_TCHFull_TCHHalf_PDCH as con-figured by OML, the regular RSL channel activation procedures can not only be used for activation of circuit-switched channels,but also for activation of a PDCH.

See Section 5.5.2.

NOTEDo not confuse this with the IPA style PDCH ACT type dynamic PDCH protocol employed by nanoBTS devices (Sec-tion 5.5.1).

5.2.2 Measurement Result

Conforms to 3GPP TS 08.58 § 8.4.8 with this limitation:

Table 23: Measurement Result IE limitations

TS 08.58 § IE Name Handling9.3.37 MS Timing Offset never sent by OsmoBTS

5.2.3 Mode Modify

Conforms to 3GPP TS 08.58 § 8.4.9 with these limitations:

Table 24: Mode Modify IE limitations

TS 08.58 § IE Name Handling9.3.45 Main channel reference ignored9.3.53 MultiRate Control ignored9.3.54 Supported Codec Types ignored

5.2.4 MS Power Control

Conforms to 3GPP TS 08.58 § 8.4.15 with these limitations:

Table 25: MS Power Control IE limitations

TS 08.58 § IE Name Handling9.3.31 MS Power Parameters ignored



5.2.5 SACCH Info Modify

Conforms to 3GPP TS 08.58 § 8.4.20, with these exceptions:

Table 26: SACCH Info Modify IE limitations

TS 08.58 § IE Name Handling9.3.30 System Info Type See below for available types9.3.23 Starting Time not supported, provokes an Error Report response

Table 27: System Info Type values that can occur on the SACCH

Value Name0x05 RSL_SYSTEM_INFO_50x06 RSL_SYSTEM_INFO_60x0d RSL_SYSTEM_INFO_5bis0x0e RSL_SYSTEM_INFO_5ter0x47 RSL_EXT_MEAS_ORDER0x48 RSL_MEAS_INFO

5.2.6 BCCH Information

Conforms to 3GPP TS 08.58 § 8.5.1, with these limitations and extensions:

Table 28: BCCH Information IE details

TS 08.58 § IE Name Handling9.3.30 System Info Type See Section 5.2.5 for available types9.3.11 L3 Info This IE may be included instead of a 9.3.39 Full BCCH Info IE. The

Full BCCH Info takes precedence over L3 Info. To stop SItransmission, both of these IEs must be omitted.

5.2.7 Channel Required

Conforms to 3GPP TS 08.58 § 8.5.3, with these limitations:

Table 29: Channel Required message IE details

TS 08.58 § IE Name Handling9.3.16 Physical Context never sent by OsmoBTS



5.2.8 Paging Command


Table 30: Paging Command message IE details

TS 08.58 § IE Name Handling9.3.49 eMLPP Priority ignored

NoteIf adding the identity to the paging queue fails, the BSC is not notified in any way.

5.3 SMS Broadcast Command


Table 31: Broadcast Command message IE details

TS 08.58 § IE Name Handling9.3.44 SMSCB Channel Indicator ignored

5.3.1 RF Resource Indication

This message does not conform to 3GPP TS 08.58 § 8.6.1, in that it omits the Resource Information IE that would contain theactual payload data, which renders this message void.

Table 32: RF Resource Indication message IE exceptions

TS 08.58 § IE Name Handling9.3.21 Resource Information OsmoBTS omits this IE, though TS 08.58 specifies it as mandatory.

5.3.2 SACCH Filling


Table 33: SACCH Filling message IE limitations

TS 08.58 § IE Name Handling9.3.30 System Info Type See Section 5.2.5 for available types9.3.23 Starting Time ignored



5.4 User Plane Transport Management

This chapter defines the A-bis/IP specific RSL procedures that are introduced in addition to the 3GPP TS 08.58 standard proce-dures.

In classic A-bis over E1, user plane traffic is carried over 16kBps sub-slots of 64kBps E1 time-slots according to ETSI/3GPP TS08.60. As the E1 line is a dedicated line between BTS and BSC, no further addressing information is required.

In A-bis/IP as described by the present document, new RSL procedures have been introduced to deal with the different propertiesof the underlying IP based transport medium.

5.4.1 RSL Create Connection (CRCX)

This procedure is used by the BSC to request the BTS to allocate + bind to a BTS-local UDP port for the subsequent transmissionof user-plane data via RTP.

To do so, the BSC sends the Create Connection (CRCX) message. In case of successful outcome, the BTS responds withCreate Connection (CRCX) ACK. In case of any error, the BTS responds with Create Connection (CRCX) NACK.

See Section 5.6.1, Section 5.6.2, Section 5.6.3

5.4.2 RSL Modify Connection (MDCX)

This procedure is used by the BSC to request the BTS to modify an already-bound BTS-local UDP port for user-plane RTP. Itis used in particular to configure the remote IP address and UDP port to which the BTS shall send user-plane RTP traffic. Thisremote address is normally either a Media Gateway (MGW) of some sort, but could also be the RTP socket of the correspondingother leg of a mobile-to-mobile call.

To modify a user-plane connection, the BSC sends the Modify Connection message. In case of successful outcome, the BTSresponds with Modify Connection (MDCX) ACK. In case of any error, the BTS responds with Modify Connection (MDCX)NACK.


5.4.3 RSL Delete Connection (DLCX)

This procedure is used by the BSC to request the BTS to delete an already-existing BTS-local UDP port for user-plane RTP.

To delete a user-plane connection, the BSC sends the Delete Connection (DLCX) message. In case of successful outcome, theBTS responds with Delete Connection (DLCX) ACK. In case of any error, the BTS responds with Delete Connection (DLCX)NACK.


5.4.4 RSL Delete Connection (DLCX) Indication

When a BTS-local UDP connection for user-plane RTP is automatically released at the time of RF CHANNEL RELEASE, theBTS sends a unilateral, non-acknowledged RSL Delete Connection (DLCX) Indication to the BSC.

See Section 5.6.7

5.5 Dynamic Channel Combinations

In the classic data model established by ETSI/3GPP for A-bis, each timeslot (channel) is configured using a static channelcombination by means of A-bis OML. Particularly in presence of GPRS services, this is very unflexible and leads to inefficientuse of air interface resources.

As such, several methods have been implemented to overcome this limitation. The fundamental operation can be outlined likethis:



• Configuration of a particular dynamic channel combination via OML

• activation of TCH works like on a classic TCH channel combination

• activation of PDCH requires some specific PDCH activation procedure

There are two variants implemented in the OsmoBTS A-bis dialect:

5.5.1 IPA Style Dynamic Channels

This method is used when OML uses NM_CHANC_IPAC_TCHFull_PDCH (0x80) as channel combination for the given time-slot.

IPA style refers to ip.access compatible PDCH activation and deactivation.

When the IPA style dynamic channel combination TCH/F or PDCH is set, the non-standard PDCH ACTIVATE (Section 5.5.1.1)and PDCH DEACTIVATE (Section 5.5.1.2) procedures are used for switching an idle channel into PDCH mode and back intoidle mode.

When the channel is used as TCH/F, regular circuit-switched activation is performed, like on any traditional TCH/F. However,the BSC must make sure to first disable the PDCH on the timeslot, before activating it as TCH/F. Likewise, any circuit-switchedTCH/F on the channel must be deactivated using standard RSL signalling, before the specific PDCH related procedures are usedto enable the PDCH.

5.5.1.1 PDCH Activate

This procedure is used by the BSC to request the BTS to activate an IPA style dynamic TCH/F+PDCH channel in PDCH mode.

The operation is not supported on any other physical channel type.


5.5.1.2 PDCH Deactivate

This procedure is used by the BSC to request the BTS to deactivate an active PDCH on any an IPA style dynamic TCH/F+PDCHchannel.

The operation is not supported on any other physical channel type.




5.5.1.3 IPA Style Dynamic Switchover Example

Figure 10: Part 1: example for dynamic channel switchover, for IPA style dynamic timeslots



Figure 11: Part 2: example for dynamic channel switchover, for IPA style dynamic timeslots

5.5.2 Osmocom Style Dynamic Channels

This method is in use when OML uses NM_CHANC_OSMO_TCHFull_TCHHalf_PDCH (0x90) for the given time-slot.

The activation of PDCH is performed by using the regular RSL CHANNEL ACTIVATE procedure according to Section 5.2.1,with these modifications:

• The C-bits part of the Channel Number IE take the non-standard binary value 11000 (C5 thru C1 as seen in 3GPP TS 08.58 §9.3.1).

• The A-bits part of the Activation Type IE take the non-standard binary value 1111, with an additional fourth bit (add A4 to A3thru A1 as seen in 3GPP TS 08.58 § 9.3.3; all remaining reserved bits as well as the R bit are coded as zero).

• The normally mandatory Channel Mode IE is omitted; none of the optional IEs are included.

Hence the message consists of exactly these IEs:

Table 34: PDCH type Channel Activation message IEs

TS 08.58 § IE Name Handling9.1 Message discriminator Dedicated Channel Management9.2 Message type CHANnel ACTIVation9.3.1 Channel number C-bits 11000, plus TS bits as usual9.3.3 Activation type A-bits 1111



5.5.2.1 Osmocom Style Dynamic Switchover Example

Figure 12: Part 1: example for dynamic channel switchover, for Osmocom style dynamic timeslots



Figure 13: Part 2: example for dynamic channel switchover, for Osmocom style dynamic timeslots

5.6 Message Formats and Contents

5.6.1 Create Connection (CRCX)

This message is sent by the BSC to the BTS to request the creation of a user-plane RTP connection for the specified Channelnumber.

INFORMATION ELEMENT REFERENCE PRESENCE FORMAT LENGTHMessage discriminator 08.58 9.1 M V 1Message type Section 5.7.1 M V 1Channel number 08.58 9.3.1 M TV 2Destination IP Address Section 5.7.4 O TV 5Destination IP Port Section 5.7.5 O TV 3IP Speech Mode Section 5.7.7 O TV 2RTP Payload Type 2 Section 5.7.11 O TV 2



5.6.2 Create Connection (CRCX) ACK

This message is sent by the BTS to the BSC to acknowledge the successful outcome of creating a user-plane RTP connection. Itis sent in response to the Create Connection (CRCX).

INFORMATION ELEMENT REFERENCE PRESENCE FORMAT LENGTHMessage discriminator 08.58 9.1 M V 1Message type Section 5.7.1 M V 1Channel number 08.58 9.3.1 M TV 2Connection Id Section 5.7.10 M TV 3Source IP Address Section 5.7.8 O TV 5Source IP Port Section 5.7.6 O TV 3RTP Payload Type 2 Section 5.7.11 O TV 2

5.6.3 Create Connection (CRCX) NACK

This message is sent by the BTS to the BSC to signal the unsuccessful outcome of creating a user-plane RTP connection. It issent in response to the Create Connection (CRCX).

INFORMATION ELEMENT REFERENCE PRESENCE FORMAT LENGTHMessage discriminator 08.58 9.1 M V 1Message type Section 5.7.1 M V 1Channel number 08.58 9.3.1 M TV 2Destination IP Address Section 5.7.4 O TV 5Destination IP Port Section 5.7.5 O TV 3Cause 08.58 9.3.26 O TLV >= 3

5.6.4 Modify Connection (MDCX)

This message is sent by the BSC to the BTS to modify the properties of a user-plane RTP connection.

INFORMATION ELEMENT REFERENCE PRESENCE FORMAT LENGTHMessage discriminator 08.58 9.1 M V 1Message type Section 5.7.1 M V 1Channel number 08.58 9.3.1 M TV 2Connection Id Section 5.7.10 O TV 3Destination IP Address Section 5.7.4 O TV 5Destination IP Port Section 5.7.5 O TV 3IP Speech Mode Section 5.7.7 O TV 2RTP Payload Type 2 Section 5.7.11 O TV 2

5.6.5 Modify Connection (MDCX) ACK

This message is sent by the BTS to the BSC to acknowledge the successful modification of a user-plane RTP connection. It issent in response to a Modify Connection (MDCX)

INFORMATION ELEMENT REFERENCE PRESENCE FORMAT LENGTHMessage discriminator 08.58 9.1 M V 1Message type Section 5.7.1 M V 1Channel number 08.58 9.3.1 M TV 2Connection Id Section 5.7.10 O TV 3Source IP Address Section 5.7.8 C TV 5Source IP Port Section 5.7.6 C TV 3RTP Payload Type 2 Section 5.7.11 O TV 2



5.6.6 Modify Connection (MDCX) NACK

This message is sent by the BTS to the BSC to signal the unsuccessful outcome of modifying the user-plane RTP connection forthe specified Channel number. It is sent in response to the Modify Connection (MDCX).

INFORMATION ELEMENT REFERENCE PRESENCE FORMAT LENGTHMessage discriminator 08.58 9.1 M V 1Message type Section 5.7.1 M V 1Channel number 08.58 9.3.1 M TV 2Cause 08.58 9.3.26 M TLV >= 3

5.6.7 Delete Connection (DLCX) Indication

This message is sent by the BTS to indicate the automatic deletion of a BTS-local UDP connection for user-plane RTP traffic atthe time of RF Channel release.

INFORMATION ELEMENT REFERENCE PRESENCE FORMAT LENGTHMessage discriminator 08.58 9.1 M V 1Message type Section 5.7.1 M V 1Channel number 08.58 9.3.1 M TV 2Connection Id Section 5.7.10 M TV 3Connection Id Section 5.7.9 M TV 3Cause 08.58 9.3.26 M TLV >= 3

5.6.8 Delete Connection (DLCX)

This message is sent by the BSC to the BTS to request the disconnection of a user-plane RTP connection for the specified Channelnumber.

INFORMATION ELEMENT REFERENCE PRESENCE FORMAT LENGTHMessage discriminator 08.58 9.1 M V 1Message type Section 5.7.1 M V 1Channel number 08.58 9.3.1 M TV 2Connection Id Section 5.7.10 O TV 3

5.6.9 Delete Connection (DLCX) ACK

This message is sent by the BTS to signal the successful outcome of deleting the user-plane RTP connection for the specifiedChannel number. It is sent in response to the Delete Connection (DLCX).

INFORMATION ELEMENT REFERENCE PRESENCE FORMAT LENGTHMessage discriminator 08.58 9.1 M V 1Message type Section 5.7.1 M V 1Channel number 08.58 9.3.1 M TV 2Connection Id Section 5.7.10 O TV 3Connection Statistics Section 5.7.9 C TV 29

5.6.10 Delete Connection (DLCX) NACK

This message is sent by the BTS to signal the unsuccessful outcome of deleting the user-plane RTP connection for the specifiedChannel number. It is sent in response to the Delete Connection (DLCX).

INFORMATION ELEMENT REFERENCE PRESENCE FORMAT LENGTHMessage discriminator 08.58 9.1 M V 1



INFORMATION ELEMENT REFERENCE PRESENCE FORMAT LENGTHMessage type Section 5.7.1 M V 1Channel number 08.58 9.3.1 M TV 2Connection Id Section 5.7.10 O TV 3Cause 08.58 9.3.26 M TLV >= 3

5.6.11 PDCH Activate

This message is sent by the BSC to request the activation of a PDCH on a IPA style dynamic TCH/F+PDCH channel.

INFORMATION ELEMENT REFERENCE PRESENCE FORMAT LENGTHMessage discriminator 08.58 9.1 M V 1Message type Section 5.7.1 M V 1Channel number 08.58 9.3.1 M TV 2

NOTEThis message is not used by Osmocom style dynamic channels

5.6.12 PDCH Activate ACK

This message is sent by the BTS to confirm the successful activation of a PDCH on a IPA style dynamic TCH/F+PDCH channel.

INFORMATION ELEMENT REFERENCE PRESENCE FORMAT LENGTHMessage discriminator 08.58 9.1 M V 1Message type Section 5.7.1 M V 1Channel number 08.58 9.3.1 M TV 2Frame Number 08.58 9.3.8 O TV 3


5.6.13 PDCH Activate NACK

This message is sent by the BTS to reject the successful activation of a PDCH on a IPA style dynamic TCH/F+PDCH channel.



5.6.14 PDCH Deactivate

This message is sent by the BSC to request the deactivation of a PDCH on a IPA style dynamic TCH/F+PDCH channel.

INFORMATION ELEMENT REFERENCE PRESENCE FORMAT LENGTHMessage discriminator 08.58 9.1 M V 1



INFORMATION ELEMENT REFERENCE PRESENCE FORMAT LENGTHMessage type Section 5.7.1 M V 1Channel number 08.58 9.3.1 M TV 2


5.6.15 PDCH Deactivate ACK

This message is sent by the BTS to confirm the successful deactivation of a PDCH on a IPA style dynamic TCH/F+PDCHchannel.

INFORMATION ELEMENT REFERENCE PRESENCE FORMAT LENGTHMessage discriminator 08.58 9.1 M V 1Message type Section 5.7.1 M V 1Channel number 08.58 9.3.1 M TV 2


5.6.16 PDCH Deactivate NACK

This message is sent by the BTS to reject the deactivation of a PDCH on a IPA style dynamic TCH/F+PDCH channel.



5.7 Information Element Codings

5.7.1 A-bis/IP specific RSL Message discriminators

The following message discriminators are used in addition to those indicated in 3GPP TS 08.58 Section 9.1:

Table 35: OsmoBTS specific new message discriminators

MessageType

Message This document §

0x70 Create Connection (CRCX) Section 5.6.10x71 Create Connection (CRCX) ACK Section 5.6.20x72 Create Connection (CRCX) NACK Section 5.6.30x73 Modify Connection (MDCX) Section 5.6.40x74 Modify Connection (MDCX) ACK Section 5.6.50x75 Modify Connection (MDCX) NACK Section 5.6.60x76 Delete Connection (DLCX) Indication Section 5.6.7




MessageType

Message This document §

0x77 Delete Connection (DLCX) Section 5.6.80x78 Delete Connection (DLCX) ACK Section 5.6.90x79 Delete Connection (DLCX) NACK Section 5.6.100x48 PDCH Activate Section 5.6.110x49 PDCH Activate ACK Section 5.6.120x4a PDCH Activate NACK Section 5.6.130x4b PDCH Deactivate Section 5.6.140x4c PDCH Deactivate ACK Section 5.6.150x4d PDCH Deactivate NACK Section 5.6.16

5.7.2 A-bis/IP specific RSL IEIs

The following Information Element Identifiers (IEIs) are used in addition to those indicated in 3GPP TS 08.58 Section 9.3:

Table 36: A-bis/IP specific information elements

IEI Name This document §0x01 RSL_IE_CHAN_NR Section 5.7.30xf0 RSL_IE_IPAC_REMOTE_IP Section 5.7.40xf1 RSL_IE_IPAC_REMOTE_PORT Section 5.7.50xf3 RSL_IE_IPAC_LOCAL_PORT Section 5.7.60xf4 RSL_IE_IPAC_SPEECH_MODE Section 5.7.70xf5 RSL_IE_IPAC_LOCAL_IP Section 5.7.80xf6 RSL_IE_IPAC_CONN_STAT Section 5.7.90xf8 RSL_IE_IPAC_CONN_ID Section 5.7.100xfc RSL_IE_IPAC_RTP_PAYLOAD2 Section 5.7.11

5.7.3 RSL_IE_CHAN_NR

This information element is coded like 3GPP TS 08.58 Section 9.3.1, but in addition supports the following extended coding:

• C5..C1 bits 0b11000 for PDCH type channels

The TN-Bits are not re-defined in this case but use the same encoding as specified in TS 08.58 Section 9.3.1.

NOTEThe above extension is only valid on an Osmocom-style dynamic channel, having configured the NM_CHANC_IPAC_TCHFull_PDCHchannel combination by OML.

5.7.4 RSL_IE_IPAC_REMOTE_IP

This information element contains the remote (MGW side) IPv4 address in network byte order. It is encoded as fixed-size elementwith one byte IEI followed by four bytes IPv4 address.



5.7.5 RSL_IE_IPAC_REMOTE_PORT

This information element contains the remote (MGW side) UDP port in network byte order. It is encoded as fixed-size elementwith one byte IEI followed by two bytes UDP port number.

5.7.6 RSL_IE_IPAC_LOCAL_PORT

This information element contains the local (BTS side) IPv4 address in network byte order. It is encoded as fixed-size elementwith one byte IEI followed by two bytes UDP port number.

5.7.7 RSL_IE_IPAC_SPEECH_MODE

This information element encodes the speech mode. It is set according to the voice codec used on the connection. It is encodedas a fixed-size element of two bytes, with one byte IEI followed by one byte Speech mode indicator.

Table 37: A-bis/IP Speech Mode Indicator Values

Value Description0x00 TCH/F with FR codec0x01 TCH/F with EFR codec0x02 TCH/F with AMR codec0x03 TCH/H with HR codec0x05 TCH/H with AMR codec

5.7.8 RSL_IE_IPAC_LOCAL_IP

This information element contains the local (BTS side) IPv4 address in network byte order. It is encoded as fixed-size elementwith one byte IEI followed by four bytes IPv4 address.

5.7.9 RSL_IE_IPAC_CONN_STAT

This information element contains statistics about the RTP connection.

It is encoded as 29 bytes, with the first byte as IEI and 28 bytes fixed-length payload encoded as follows:

Table 38: A-bis/IP Connection Statistics

Offset Size Description0 4 Total number of RTP packets sent4 4 Total number of octets sent8 4 Total number of RTP packets received12 4 Total number of octets received16 4 Total number of lost packets in Rx direction20 4 Inter-arrival Jitter24 4 Average transmission delay

All the above values are encoded in network byte order.

A detailed definition of the individual values is given in RFC 1889.



5.7.10 RSL_IE_IPAC_CONN_ID

This IE is a TV with a value length of two bytes. The value is a 16 bit connection ID in network byte order.

5.7.11 RSL_IE_IPAC_RTP_PAYLOAD2

This information element contains the RTP payload identifier, which is used in the PT (Payload Type) field of the RTP header insubsequent transmissions of the RTP flow.

5.8 A-bis RSL Initialization / BTS bring-up

Upon receiving the IPA RSL CONNECT OML message by the respective Baseband Transceiver MO, the BTS proceeds withestablishing a separate TCP connection for the given TRX.

Figure 14: A-bis RSL BTS bring-up for primary TRX



Figure 15: A-bis RSL BTS bring-up for secondary TRXs

The initialization of the primary and secondary TRX slightly differ, as illustrated by the differences of Figure 14 and Figure 15.Since the secondary TRX has no BCCH, it does not (need to) receive any RSL BCCH INFORMATION messages from the BSC.

6 User-Plane Traffic via RTP

RTP (Realtime Transfer Protocol) is a protocol for streaming audio and video data. It is specified by IETF RFC 1889.

OsmoBTS A-bis/IP implements RTP as transport medium for circuit-switched user-plane traffic, contrary to the E1 sub-slotbased transport specified in 3GPP TS 08.60.

The RTP transport endpoint parameters are configured using the RSL User Plane Transport Management procedures describedin Section 5.4.

RTCP is implemented in addition to RTP, on a UDP port number of the RTP port incremented by one.

6.1 RTP Payload Formats

The RTP payload format depends on the voice codec used on the radio channel. The OsmoBTS is simply passing the GSMspeech frames between the Um radio interface channels and the RTP payload (and vice-versa).

No transcoding function is implemented in the BTS!

Table 39: RTP Payload formats

TCH Codec RTP payload format specificationTCH/F FR IETF RFC 3551 Section 4.5.8TCH/F EFR IETF RFC 3551 Section 4.5.9TCH/F AMR IETF RFC 4867TCH/H HR IETF RFC 5993TCH/H AMR IETF RFC 4867



7 Glossary

2FF2nd Generation Form Factor; the so-called plug-in SIM form factor

3FF3rd Generation Form Factor; the so-called microSIM form factor

3GPP3rd Generation Partnership Project

4FF4th Generation Form Factor; the so-called nanoSIM form factor

A InterfaceInterface between BTS and BSC, traditionally over E1 (3GPP TS 48.008 [?])

A3/A8Algorithm 3 and 8; Authentication and key generation algorithm in GSM and GPRS, typically COMP128v1/v2/v3 orMILENAGE are typically used

A5Algorithm 5; Air-interface encryption of GSM; currently only A5/0 (no encryption), A5/1 and A5/3 are in use

Abis InterfaceInterface between BTS and BSC, traditionally over E1 (3GPP TS 48.058 [?] and 3GPP TS 52.021 [?])

ACCAccess Control Class; every BTS broadcasts a bit-mask of permitted ACC, and only subscribers with a SIM of matchingACC are permitted to use that BTS

AGCHAccess Grant Channel on Um interface; used to assign a dedicated channel in response to RACH request

AGPLGNU Affero General Public License, a copyleft-style Free Software License

ARFCNAbsolute Radio Frequency Channel Number; specifies a tuple of uplink and downlink frequencies

AUCAuthentication Center; central database of authentication key material for each subscriber

BCCHBroadcast Control Channel on Um interface; used to broadcast information about Cell and its neighbors

BCCBase Station Color Code; short identifier of BTS, lower part of BSIC

BTSBase Transceiver Station

BSCBase Station Controller

BSICBase Station Identity Code; 16bit identifier of BTS within location area



BSSGPBase Station Subsystem Gateway Protocol (3GPP TS 48.018 [?])

BVCIBSSGP Virtual Circuit Identifier

CBCHCell Broadcast Channel; used to transmit Cell Broadcast SMS (SMS-CB)

CCCall Control; Part of the GSM Layer 3 Protocol

CCCHCommon Control Channel on Um interface; consists of RACH (uplink), BCCH, PCH, AGCH (all downlink)

CellA cell in a cellular network, served by a BTS

CEPTConférence européenne des administrations des postes et des télécommunications; European Conference of Postal andTelecommunications Administrations.

CGICell Global Identifier comprised of MCC, MNC, LAC and BSIC

dBdeci-Bel; relative logarithmic unit

dBmdeci-Bel (milliwatt); unit of measurement for signal strength of radio signals

DHCPDynamic Host Configuration Protocol (IETF RFC 2131 [?]

downlinkDirection of messages / signals from the network core towards the mobile phone

DSPDigital Signal Processor

dvnixloadTool to program UBL and the Bootloader on a sysmoBTS

EDGEEnhanced Data rates for GPRS Evolution; Higher-speed improvement of GPRS; introduces 8PSK

EGPRSEnhanced GPRS; the part of EDGE relating to GPRS services

ESMEExternal SMS Entity; an external application interfacing with a SMSC over SMPP

ETSIEuropean Telecommunications Standardization Institute

FPGAField Programmable Gate Array; programmable digital logic hardware

GbInterface between PCU and SGSN in GPRS/EDGE network; uses NS, BSSGP, LLC

GERANGPRS/EDGE Radio Access Network



GFDLGNU Free Documentation License; a copyleft-style Documentation License

GGSNGPRS Gateway Support Node; gateway between GPRS and external (IP) network

GMSKGaussian Minimum Shift Keying; modulation used for GSM and GPRS

GPLGNU General Public License, a copyleft-style Free Software License

GpGp interface between SGSN and GGSN; uses GTP protocol

GPSGlobal Positioning System; provides a highly accurate clock reference besides the global position

GSMGlobal System for Mobile Communications. ETSI/3GPP Standard of a 2G digital cellular network

GSMTAPGSM tap; pseudo standard for encapsulating GSM protocol layers over UDP/IP for analysis

GTGlobal Title; an address in SCCP

GTPGPRS Tunnel Protocol; used between SGSN and GGSN

HLRHome Location Register; central subscriber database of a GSM network

HPLMNHome PLMN; the network that has issued the subscriber SIM and has his record in HLR

IEInformation Element

IMEIInternational Mobile Equipment Identity; unique identifier for the mobile phone

IMSIInternational Mobile Subscriber Identity; 15-digit unique identifier for the subscriber/SIM; starts with MCC/MNC ofissuing operator

IPInternet Protocol (IETF RFC 791 [?])

IPAip.access GSM over IP protocol; used to multiplex a single TCP connection

LACLocation Area Code; 16bit identifier of Location Area within network

LAPDLink Access Protocol, D-Channel (ITU-T Q.921 [?])

LAPDmLink Access Protocol Mobile (3GPP TS 44.006 [?])

LLCLogical Link Control; GPRS protocol between MS and SGSN (3GPP TS 44.064 [?])



Location AreaLocation Area; a geographic area containing multiple BTS

M2PAMTP2 Peer-to-Peer Adaptation; a SIGTRAN Variant (RFC 4165 [?])

M2UAMTP2 User Adaptation; a SIGTRAN Variant (RFC 3331 [?])

M3UAMTP3 User Adaptation; a SIGTRAN Variant (RFC 4666 [?])

MCCMobile Country Code; unique identifier of a country, e.g. 262 for Germany

MFFMachine-to-Machine Form Factor; a SIM chip package that is soldered permanently onto M2M device circuit boards.

MGWMedia Gateway

MMMobility Management; part of the GSM Layer 3 Protocol

MNCMobile Network Code; identifies network within a country; assigned by national regulator

MNOMobile Network Operator; operator with physical radio network under his MCC/MNC

MSMobile Station; a mobile phone / GSM Modem

MSCMobile Switching Center; network element in the circuit-switched core network

MSISDNMobile Subscriber ISDN Number; telephone number of the subscriber

MTPMessage Transfer Part; SS7 signaling protocol (ITU-T Q.701 [?])

MVNOMobile Virtual Network Operator; Operator without physical radio network

NCCNetwork Color Code; assigned by national regulator

NITBNetwork In The Box; combines functionality traditionally provided by BSC, MSC, VLR, HLR, SMSC functions; seeOsmoNITB

NSEINS Entity Identifier

NVCINS Virtual Circuit Identifier

NWLNetwork Listen; ability of some BTS to receive downlink from other BTSs

NSNetwork Service; protocol on Gb interface (3GPP TS 48.016 [?])



OCXOOven Controlled Crystal Oscillator; very high precision oscillator, superior to a VCTCXO

OMLOperation & Maintenance Link (ETSI/3GPP TS 52.021 [?])

OpenBSCOpen Source implementation of GSM network elements, specifically OsmoBSC, OsmoNITB, OsmoSGSN

OpenGGSNOpen Source implementation of a GPRS Packet Control Unit

OpenVPNOpen-Source Virtual Private Network; software employed to establish encrypted private networks over untrusted publicnetworks

OsmocomOpen Source MObile COMmunications; collaborative community for implementing communications protocols and sys-tems, including GSM, GPRS, TETRA, DECT, GMR and others

OsmoBSCOpen Source implementation of a GSM Base Station Controller

OsmoNITBOpen Source implementation of a GSM Network In The Box, combines functionality traditionally provided by BSC, MSC,VLR, HLR, AUC, SMSC

OsmoSGSNOpen Source implementation of a Serving GPRS Support Node

OsmoPCUOpen Source implementation of a GPRS Packet Control Unit

OTAOver-The-Air; Capability of operators to remotely reconfigure/reprogram ISM/USIM cards

PCPoint Code; an address in MTP

PCHPaging Channel on downlink Um interface; used by network to page an MS

PCUPacket Control Unit; used to manage Layer 2 of the GPRS radio interface

PDCHPacket Data Channel on Um interface; used for GPRS/EDGE signalling + user data

PINPersonal Identification Number; a number by which the user authenticates to a SIM/USIM or other smart card

PLMNPublic Land Mobile Network; specification language for a single GSM network

PUKPIN Unblocking Code; used to unblock a blocked PIN (after too many wrong PIN attempts)

RACRouting Area Code; 16bit identifier for a Routing Area within a Location Area

RACHRandom Access Channel on uplink Um interface; used by MS to request establishment of a dedicated channel



RAMRemote Application Management; Ability to remotely manage (install, remove) Java Applications on SIM/USIM Card

RFRadio Frequency

RFMRemote File Management; Ability to remotely manage (write, read) files on a SIM/USIM card

RoamingProcedure in which a subscriber of one network is using the radio network of another network, often in different countries;in some countries national roaming exists

Routing AreaRouting Area; GPRS specific sub-division of Location Area

RRRadio Resources; Part of the GSM Layer 3 Protocol

RSLRadio Signalling Link (3GPP TS 48.058 [?])

RTPReal-Time Transport Protocol (IETF RFC 3550 [?]); Used to transport audio/video streams over UDP/IP

SACCHSlow Associate Control Channel on Um interface; bundled to a TCH or SDCCH, used for signalling in parallel to activededicated channel

SCCPSignaling Connection Control Part; SS7 signaling protocol (ITU-T Q.711 [?])

SDCCHSlow Dedicated Control Channel on Um interface; used for signalling and SMS transport in GSM

SDKSoftware Development Kit

SIGTRANSignaling Transport over IP (IETF RFC 2719 [?])

SIMSubscriber Identity Module; small chip card storing subscriber identity

SiteA site is a location where one or more BTSs are installed, typically three BTSs for three sectors

SMPPShort Message Peer-to-Peer; TCP based protocol to interface external entities with an SMSC

SMSCShort Message Service Center; store-and-forward relay for short messages

SS7Signaling System No. 7; Classic digital telephony signaling system

SSHSecure Shell; IETF RFC 4250 [?] to 4254

SSNSub-System Number; identifies a given SCCP Service such as MSC, HLR

STPSignaling Transfer Point; A Router in SS7 Networks



SUASCCP User Adaptation; a SIGTRAN Variant (RFC 3868 [?])

syslogSystem logging service of UNIX-like operating systems

System InformationA set of downlink messages on the BCCH and SACCH of the Um interface describing properties of the cell and network

TCHTraffic Channel; used for circuit-switched user traffic (mostly voice) in GSM

TCPTransmission Control Protocol; (IETF RFC 793 [?])

TFTPTrivial File Transfer Protocol; (IETF RFC 1350 [?])

TRXTransceiver; element of a BTS serving a single carrier

u-BootBoot loader used in various embedded systems

UBIAn MTD wear leveling system to deal with NAND flash in Linux

UBLInitial bootloader loaded by the TI Davinci SoC

UDPUser Datagram Protocol (IETF RFC 768 [?])

UICCUniversal Integrated Chip Card; A smart card according to ETSI TR 102 216 [?]

Um interfaceU mobile; Radio interface between MS and BTS

uplinkDirection of messages: Signals from the mobile phone towards the network

USIMUniversal Subscriber Identity Module; application running on a UICC to provide subscriber identity for UMTS and GSMnetworks

VCTCXOVoltage Controlled, Temperature Compensated Crystal Oscillator; a precision oscillator, superior to a classic crystal oscil-lator, but inferior to an OCXO

VPLMNVisited PLMN; the network in which the subscriber is currently registered; may differ from HPLMN when on roaming

VTYVirtual TeletYpe; a textual command-line interface for configuration and introspection, e.g. the OsmoBSC configurationfile as well as its telnet link on port 4242

A Osmocom TCP/UDP Port Numbers

The Osmocom GSM system utilizes a variety of TCP/IP based protocols. The table below provides a reference as to which portnumbers are used by which protocol / interface.



Table 40: TCP/UDP port numbers

L4Protocol

PortNumber

Purpose Software

UDP 2427 MGCP GW osmo-bsc_mgcp, osmo-mgwTCP 2775 SMPP (SMS interface for external programs) osmo-nitbTCP 3002 A-bis/IP OML osmo-bts, osmo-bsc, osmo-nitbTCP 3003 A-bis/IP RSL osmo-bts, osmo-bsc, osmo-nitbTCP 4239 telnet (VTY) osmo-stpTCP 4240 telnet (VTY) osmo-pcuTCP 4241 telnet (VTY) osmo-btsTCP 4242 telnet (VTY) osmo-nitb, osmo-bsc, cellmgr-ngTCP 4243 telnet (VTY) osmo-bsc_mgcp, osmo-mgwTCP 4244 telnet (VTY) osmo-bsc_natTCP 4245 telnet (VTY) osmo-sgsnTCP 4246 telnet (VTY) osmo-gbproxyTCP 4247 telnet (VTY) OsmocomBBTCP 4249 Control Interface osmo-nitb, osmo-bscTCP 4250 Control Interface osmo-bsc_natTCP 4251 Control Interface osmo-sgsnTCP 4252 telnet (VTY) sysmobts-mgrTCP 4253 telnet (VTY) osmo-gtphubTCP 4254 telnet (VTY) osmo-mscTCP 4255 Control Interface osmo-mscTCP 4256 telnet (VTY) osmo-sip-connectorTCP 4257 Control Interface osmo-ggsn, ggsn (OpenGGSN)TCP 4258 telnet (VTY) osmo-hlrTCP 4259 Control Interface osmo-hlrTCP 4260 telnet (VTY) osmo-ggsnTCP 4261 telnet (VTY) osmo-hnbgwTCP 4262 Control Interface osmo-hnbgwUDP 4729 GSMTAP Almost every osmocom projectTCP 5000 A/IP osmo-bsc, osmo-bsc_natUDP 2427 GSMTAP osmo-pcu, osmo-btsUDP 23000 GPRS-NS over IP default port osmo-pcu, osmo-sgsn, osmo-gbproxy

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B.11 FUTURE REVISIONS OF THIS LICENSE

The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time.Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.See http://www.gnu.org/copyleft/.


http://www.gnu.org/copyleft/


Each version of the License is given a distinguishing version number. If the Document specifies that a particular numberedversion of this License “or any later version” applies to it, you have the option of following the terms and conditions either ofthat specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If theDocument does not specify a version number of this License, you may choose any version ever published (not as a draft) by theFree Software Foundation. If the Document specifies that a proxy can decide which future versions of this License can be used,that proxy’s public statement of acceptance of a version permanently authorizes you to choose that version for the Document.

B.12 RELICENSING

“Massive Multiauthor Collaboration Site” (or “MMC Site”) means any World Wide Web server that publishes copyrightableworks and also provides prominent facilities for anybody to edit those works. A public wiki that anybody can edit is an exampleof such a server. A “Massive Multiauthor Collaboration” (or “MMC”) contained in the site means any set of copyrightable worksthus published on the MMC site.

“CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, anot-for-profit corporation with a principal place of business in San Francisco, California, as well as future copyleft versions ofthat license published by that same organization.

“Incorporate” means to publish or republish a Document, in whole or in part, as part of another Document.

An MMC is “eligible for relicensing” if it is licensed under this License, and if all works that were first published under thisLicense somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no covertexts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.

The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time beforeAugust 1, 2009, provided the MMC is eligible for relicensing.

B.13 ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyrightand license notices just after the title page:

Copyright (c) YEAR YOUR NAME.Permission is granted to copy, distribute and/or modify this documentunder the terms of the GNU Free Documentation License, Version 1.3or any later version published by the Free Software Foundation;with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.A copy of the license is included in the section entitled ``GNUFree Documentation License''.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with. . . Texts.” line with this:

with the Invariant Sections being LIST THEIR TITLES, with theFront-Cover Texts being LIST, and with the Back-Cover Texts being LIST.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suitthe situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under yourchoice of free software license, such as the GNU General Public License, to permit their use in free software.


Documents

OsmoBTS Abis Protocol Specification